Wireless power transmission may include a transmitter for forming and directing radio frequency (RF) waves towards a receiver which may convert RF waves into usable power for charging or powering an electronic device. The receiver may be integrated in the electronic device (e.g., a smartphone, a tablet) or may be in the form of cases that may be operatively coupled with the electronic device for suitable charging or powering. The transmitter may include an antenna array composed of a plurality of directional antennas.
The antenna arrays may be controlled by computer hardware and software in order to broadcast a wireless signal towards the receiver. Amplitude and phase among other properties of the transmitted RF waves may be tuned by the computer hardware and software to form constructive and destructive interference patterns generating pockets of energy in a 3-dimensional shape from the constructive patterns, and null spaces from the destructive patterns to aim the pockets of energy to specific receivers.
The number of antennas in the antenna arrays may vary in relation with the desired power range and transmission capability of the transmitter. The more antennas in the array, the wider the range and higher the power transmission potential available at the transmitter. More antennas may additionally enable the transmitter to target more receivers at once. Directional antenna designs that can be integrated in transmitters may include Yagi, log-periodic, corner reflectors, and parabolic antennas, among others.
However, size may be one important factor that may impact the number of antennas that can be integrated in the antenna arrays for the transmitter. Designers often look for the optimal combination of size and performance in the antennas integrated in the transmitter, where the performance is usually hampered when size is reduced.
Planar inverted-F antennas (PIFA) may be fabricated in small form factors that may allow for dense antenna arrays. However, PIFA antenna's radiation pattern is commonly omnidirectional, and as a result, it may waste transmitted power if included in the transmitter. Additionally, the omnidirectional radiation patterns may hinder the transmitter ability to focus the transmitted RF waves to specific receivers.
Although other antennas designs may provide significant gain, arrays of independently fed antennas may provide a transmitter with flexibility of control. Flexible control may allow for the formation of highly directional lobes and pocket forming which may lead to more efficiency obtained from the antenna arrays.
For the foregoing reasons, there is a need for a plurality of directional antennas that could be formed on arrays of reasonably small size while keeping a suitable performance, and that could be controlled and fed independently on the arrays.